Artificial Evolution and Mageta the Lion Creature Type Change Magic

If someone activates Mageta the Lion can I respond with Artificial Evolution changing "Lion" to something else (like Elf?) so now the ability says "Destroy all creatures except for Mageta the Elf, and Mageta the Lion will be destroyed?

No. First of all, Lion isn't a creature type. Second of all, when a card refers to itself by name, it just means the card that the ability is on. Third of all, Artificial Evolution doesn't affect words in the card's name, not even in the text box. Finally, even if you could do this, Artificial Evolution would change all instances of the creature type, meaning that the ability would say "except for Mageta the Elf", and the card's name would be Mageta the Elf, which would accomplish exactly nothing.